1. Field of the Invention
The present invention relates to a magnetic recording medium whose recording layer includes a recording magnetic region of a predetermined pattern. The present invention also relates to a method of making such a magnetic recording medium.
2. Description of the Related Art
A magnetic disk (magnetic recording medium) is well known as one of recording media that constitute storage apparatus such as a hard disk. The magnetic disk has a multilayer structure including a disk substrate and a recording layer with a predetermined magnetic structure. The ongoing increase in amount of information to be processed by a computer system is creating greater demand for a higher recording density from the magnetic disk.
When recording information on the magnetic disk, a magnetic head for recording is disposed close to a recording surface of the magnetic disk (so as to float thereabove), and the magnetic head applies to the recording layer a recording magnetic field stronger than the coercivity thereof. Sequentially reversing the direction of the recording magnetic field applied by the magnetic head while relatively moving the magnetic head with respect to the magnetic disk leads to formation of a plurality of recording marks (magnetic domains), alternately magnetized in opposite directions, aligned circumferentially of the disk-along an information track of the recording layer. Controlling the timing to reverse the direction of the recording magnetic field during this process enables forming each recording mark in a predetermined length. Thus on the recording layer, a predetermined signal or information is recorded based on variation of the magnetizing direction.
In the field of the magnetic disk, the magnetic disks including a recording layer having a recording magnetic region of a predetermined pattern have been developed for achieving higher recording density, such as a so-called discrete track medium (hereinafter, DTM) and patterned medium (PM). Such magnetic disks can be found, for example, in Patent documents 1 to 3 listed below.
Patent document 1: JP-A-2005-71467
Patent document 2: JP-A-2005-166115
Patent document 3: JP-A-2005-293730
FIGS. 21 and 22 depict a magnetic disk 40, which is the DTM. FIG. 21 is a plan view of the magnetic disk 40, and FIG. 32 is an enlarged fragmentary cross-sectional view taken along a radial direction of the magnetic disk 40.
The magnetic disk 40 has a multilayer structure including a disk substrate 41, a recording layer 42, and a cover layer 43 (not shown in FIG. 21). The recording layer 42 includes a plurality of recording magnetic regions 42A and a plurality of non-magnetic regions 42B. The recording magnetic regions 42A are concentrically disposed on the disk substrate 4 around a common center that coincides with the rotational axial center A′ of the magnetic disk 40, as schematically partially indicated by bold lines in FIG. 21, thereby respectively constituting an information track. The non-magnetic regions 42B are interposed between the recording magnetic regions 42A. The exposed surface of the cover layer 43 constitutes a recording surface 44 of the magnetic disk 40.
When recording information on the magnetic disk 40 thus constructed, the recording magnetic head is disposed so as to float above the recording surface 44 of the magnetic disk 40 and applies the recording magnetic field, thus to create a plurality of recording marks (magnetic domains), alternately magnetized in opposite directions and serially aligned circumferentially of the disk, in one of the recording magnetic regions 42A of the recording layer 42.
FIGS. 23(a) to 24(d) depict a conventional manufacturing method of the magnetic disk 40. To manufacture the magnetic disk 40, firstly a predetermined magnetic material is deposited on the disk substrate 41 by a sputtering process for example, so that a magnetic film 42A′ is formed as shown in FIG. 23(a). Then as shown in FIG. 23(b), a photoresist layer 51 is formed on the magnetic film 42A′. A lithography process is then performed so as to form a resist pattern 52 from the photoresist layer 51, as shown in FIG. 23(c). The resist pattern 52 is provided with openings 52a located according to the pattern of the non-magnetic region 42B of the recording layer 42. The resist pattern 52 also includes openings (not shown) located according to the pattern of the non-magnetic region 42B. To be more detailed, in the lithography process a predetermined pattern (latent image) is formed by exposure on the photoresist layer 51 with an exposure equipment, after which the photoresist layer 51 is developed. The resist pattern 52 is thus formed on the magnetic film 42A′. Proceeding to FIG. 23(d), a predetermined etching process is performed on the magnetic film 42A′ utilizing the resist pattern 52 as the mask, to thereby delineate the pattern of the magnetic film 42A.
Proceeding to FIG. 24(a), the resist pattern 52 is removed. A non-magnetic material 42B′ is then deposited as shown in FIG. 24(b). More specifically, for example a sputtering process is performed to deposit the non-magnetic material 42B′ over the recording magnetic regions 42A including the gaps formed therebetween. Then as shown in FIG. 24(c), the non-magnetic material 42B′ is partially removed by mechanical polishing except for a portion between the recording magnetic regions 42A. Upon completion of this process, the non-magnetic region 42B′ is formed and thus the recording layer 42 is obtained. This is followed by deposition of a predetermined material on the recording layer 42, for example by a CVD or sputtering process, so that the cover layer 43 is formed as shown in FIG. 24(d). The foregoing process provides the magnetic disk 40 including the recording layer 42 having the recording magnetic region 42A of the predetermined pattern.
Such process, however, does not provide sufficient flatness on the recording surface 44. According to the foregoing process, after forming the recording magnetic region 42A in the predetermined pattern by etching on the magnetic film 42A′ as described referring to FIG. 23(d), the non-magnetic material 42B′ is deposited so as to fill in the gaps between the recording magnetic regions 42A as shown in FIG. 24(b), and then the mechanical polishing is performed to remove the excessive portion of the non-magnetic material 42B′ is removed thus to form the recording layer 42 as shown in FIG. 24(c). The upper surface of the recording layer 42 thus formed is of a non-continuous film structure which is difficult to be formed with sufficient flatness, and since the surface flatness of the recording layer 42 is reflected in the recording surface 44, it is difficult to attain sufficient flatness on the recording surface 44.
Generally, the magnetic head that floats above the magnetic disk when recording or reproducing information is required to define a lower floating height (distance between the magnetic head and the recording surface), when the in-plane or longitudinal recording density of the magnetic disk, or more specifically the recording layer is higher. Accordingly, in order for the magnetic head to work properly at a lower floating height, the recording surface of the magnetic disk has to be sufficiently flat. Consequently, the lower the required floating height is (i.e. the higher the in-plane recording density is), the higher level of flatness is required from the recording surface.
However as already stated, the conventional manufacturing method as described above does not provide sufficient flatness on the recording layer 42, and hence the recording surface 44. The magnetic disk 40 obtained through such manufacturing method is, therefore, not desirable in reducing the floating height of the magnetic head, i.e. in attaining higher recording density.
Besides, the foregoing method is not suitable for mass production of the magnetic disk 40, from the viewpoint of production efficiency. According to the foregoing method, a predetermined thin film formation process is performed in a predetermined chamber set at a predetermined degree of vacuum, to form the magnetic film 42A′ as shown in FIG. 23(a), to deposit the non-magnetic material 42B′ as shown in FIG. 24(b), and to form the cover layer 43 as shown in FIG. 24(d). However, whereas the photoresist layer 51 has to be formed in a predetermined pattern and again the magnetic film 42A′ has to be patterned by etching as described referring to FIG. 23(d), so as to obtain the recording magnetic region 42A from the magnetic film 42A′, the magnetic disk under process has to be once taken out of the chamber after forming the magnetic film 42A′ under a vacuum, when executing those processes. Further, whereas a polishing apparatus has to be employed for removing the excessive portion of the non-magnetic material 42B′ as described referring to FIG. 24(c), the disk under process has to be taken out of the chamber after depositing the non-magnetic material 42B′ under a vacuum, in order to execute the polishing. Thus, according to the foregoing method, the magnetic disk under process has to be taken out of the chamber between the formation of the magnetic film 42A′ and deposition of the non-magnetic material 42B′, as well as between the deposition of the non-magnetic material 42B′ and formation of the cover layer 43, on the production line, which inhibits arranging an in-line production process that includes these series of steps. The foregoing method is, consequently, undesirable when executing mass production of the magnetic disk 40, because those series of steps cannot be arranged in a successive line.
In addition, the step relevant to FIG. 24(b) requires depositing a considerable amount of material has to be deposited to form the non-magnetic material 42B′, and the step relevant to FIG. 24(c) imposes severe technical difficulty in detecting that the mechanical polishing has been performed to the level of the upper surface of the recording magnetic region 42A and stopping the polishing action at that moment. These are additional disadvantages in adopting the foregoing method for mass production of the magnetic disk 40.